Right ventricular failure (RVF) is a serious clinical problem with a poor prognosis. However, specific treatment options for RVF are very limited. Recent studies suggest that powerful cardioprotective effects are mediated by ?1-adrenergic receptors, in particular the ?1A-subtype (?1A-AR). In the current funding period, we found that chronic stimulation of ?1A-ARs had major beneficial effects on RV function in two mouse models of RVF induced by pulmonary fibrosis or pulmonary artery constriction (PAC). This renewal project will identify the mechanisms involved in ?1A-AR-mediated reversal of RVF and investigate if the beneficial effects of chronic ?1A-AR stimulation extend to beneficial effects in human cardiac muscle preparations. This renewal project will build on the following preliminary results from the current funding period: In a model of RVF induced by PAC, RVF was reversed by chronic treatment with a highly specific ?1A- AR agonist (A61603), at a low dose that did not raise blood pressure. The beneficial effect of A61603 treatment involved increased signaling by the pro-survival kinase ERK, increased BCL-2 (anti-apoptosis factor that protects mitochondria), increased myocardial ATP levels, and decreased levels of reactive oxygen species (ROS), suggesting protective effects on mitochondria. RVF was associated with increased abundance of a novel intracellular isoform of matrix- metalloproteinase-2: N-terminal truncated MMP-2 (NTT-MMP-2). NTT-MMP-2 expression was reported to be induced by ROS and result in mitochondrial dysfunction, decreased ATP production and further ROS generation. Our preliminary results show that A61603 treatment reduces NTT-MMP-2 in mitochondria, and increased myocardial ATP, suggesting improved mitochondrial function. In the PAC model of RVF, chronic A61603 treatment decreased ROS, decreased ROS-mediated modification of myofilament proteins and increased myofilament force development. Preliminary studies using computational modeling suggest that increased myofilament force development is a critical factor in the improved RV function resulting from A61603 treatment. We recently reported that the ?1A-AR mediates a robust inotropic response in human RV myocardium from heart failure patients and that ?1A-AR-ERK signaling is present in failing human myocardium. These findings suggest that the ?1A-AR is present and functional in failing human RV and might be a therapeutic target to induce cardioprotective effects in patients with RVF. Hypothesis 1. For failing RV, chronic A61603 treatment rescues mitochondrial bioenergetic function, resulting in increased ATP levels, reduced ROS generation and increased contraction. Hypothesis 2. Rescue of mitochondrial bioenergetic function is mediated by reduced NTT-MMP-2 levels. Hypothesis 3. Chronic ?1A-AR stimulation is beneficial in human cardiac muscle preparations. Aim 1. Determine if chronic A61603 treatment of RVF rescues mitochondrial bioenergetic function; leading to increased ATP levels, reduced ROS levels, increased myofilament contraction and rescue of RVF. Aim 2. Determine if rescue of mitochondrial function is mediated by reduced levels of NTT-MMP-2. We will determine if chronic A61603 treatment of RVF reduces levels of NTT-MMP-2 and thereby rescues mitochondrial function. We will determine if inhibiting NTT-MMP-2 experimentally rescues mitochondrial function. Aim 3. Determine if chronic treatment with A61603 has beneficial effects in human cardiac muscle preparations. As proof of principle for translation to humans, we will determine if chronic A61603 treatment has beneficial effects in two cardiac muscle preparations: engineered human heart tissue containing induced pluripotent stem cell (iPSC)-derived cardiomyocytes, and cultured RV trabeculae from RVF patients.